Outward curved or ridged premix burner membranes, e.g. as known from WO 2004/092647 in the name of the applicant, especially the two ridged burner membranes, have proven to be very efficient in high load premix applications. The flame patterns produced by outward curved burner surfaces and ridged burner surfaces are defined by a lateral extending flame front. These burner membranes are designed for heavy load burning generating minimal amounts of CO and NOx. However, when these burners are mounted into a combustion chamber, still higher levels of CO and NOx are reached because of the available combustion volume in the combustion chamber and/or the combustion chamber interior design. High CO-values are created when the flame comes in direct contact with cold surfaces, thereby ending the combustion reaction too early. In a V-shaped combustion room of most state of the art heat exchangers the V-shape flame is burning directly onto the cold walls of the V-shaped combustion room. In such a V-shaped combustion room dead spaces are always created at the top directly besides the burner flame. High NOx values on the other hand are created when flue gasses are overheated, for example by recirculation of hot flue gasses due to irregular shape of the combustion room (dead angles). These constraints therefore hinder compaction of the combustion chamber, in spite of the compaction of the burner membrane.
It would be desirable to have a combustion chamber wherein complete combustion, without creation of undesirable combustion products, is guaranteed in the smallest volume attainable.